How to initialize a list?

[xavier nayrac]

New to Elixir, I'm trying to initialize a List of 100 elements, all set to false.
Here is what I have:

a = []
Enum.each 1..10, fn _ ->
  a = a ++ [false]    
end

I try this too:

Enum.each 1..10, fn _ ->
  List.insert_at a, 0, false
end

But 'a' doesn't change. I think I don't understand how immutable things works...
Does someone could give me a clue?

[atkaaz]

maybe this?

Enum.each 1..10, fn _ ->

  a = List.insert_at a, 0, false
end

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[José Valim]

Enum.map 1..100, fn _ -> false end

In this example, we are mapping over each value in the range, transforming them into false.

Doing iteration in Elixir is different than in imperative languages. You rarely want to call each for example, because as you noticed, the value of a doesn't change.

The Introducing Erlang and the equivalent Introducing Elixir book are great resources into pattern matching, recursion and other functionality found in functional programming languages.

José Valim

www.plataformatec.com.br

Skype: jv.ptec

Founder and Lead Developer

--

[xavier nayrac]

Thank you, guys.

[atkaaz]

I kind of expected this to work too:

iex(8)> lc n inlist 1..10, do: false
** (ErlangError) erlang error: {:bad_generator, 1..10}
    :erl_eval.expr/3

but only something like this would work:
iex(8)> lc n inlist [1,2,3], do: false
[false, false, false]
iex(9)> lc n inlist [1..10], do: false
[false]

[atkaaz]

I am sort of explaining this to myself by this:

a = []
Enum.each 1..10, fn _ ->

  IO.puts inspect a

  a = a ++ [false]   

  IO.puts inspect a
end

outputs:
[]
[false]
[]
[false]
[]
[false]
[]
[false]
[]
[false]
[]
[false]
[]
[false]
[]
[false]
[]
[false]
[]
[false]
:ok

What is this called? similar to macro hygiene but it's something else, closure? or something with (local)scope?

[Eric Meadows-Jönsson]

inlist only works on lists. 1..10 is a record that implements Enumerable. An inenum operator will probably come and then your example will work. lc n inlist [1..10], do: false doesnt work because you create a list the looks like this [Range[first: 1, last: 10]] with only one element.

Eric Meadows-Jönsson

[atkaaz]

Thank you. I figured the one element part but had no idea about everything else. Much appreciated.